This invention relates to a pultruded part reinforced by longitudinal and transverse fibers and a method of manufacturing the part.
Pultrusion is a technique in which longitudinally continuous fibrous structures are used to pull a resin through a die so that the resin sets and produces a rigid part downstream of the die to which the pulling force is applied.
Originally the longitudinal fibres consisted of simply longitudinal in the extending rovings and the parts were of a relatively simple cross section such as rods, T-bars and the like. However developments have been introduced to reduce the wall thickness of the parts so that complex cross sections including hollow cross sections could be manufactured. In order to achieve the necessary strength of the parts, it was necessary to introduce transverse fibers to provide strength in the transverse direction. Such transverse fibers are conventionally applied using a mat of a woven or non woven material. In many cases the fibers in the mat are generally random so that the number of fibers extending in the transverse direction is relatively small. One major problem with the mat is that it is relatively expensive and can be very expensive so that it is more than double per pound of the cost of the simple conventional rovings. One direction of development has been to provide improved mats which apply more of the fibers in the transverse direction thus allowing the mat to be of reduced thickness to provide the required strength or toughness in the finished part. An example of a mat tailored for pultrusion is shown in published International application PCT/WO78529A1 published Dec. 28, 2000 and assigned to Pella.
An alternative approach to the expense of the mat is to attempt to attach to the longitudinal rovings some transverse fibers which are simply chopped roving material. One example of an arrangement of this type is shown in U.S. Pat. No. 5,324,377 of the present inventor Davies. This method of pultrusion attempted to attach transverse fibers to the outside of a body of longitudinal rovings so as to be carried through the die with the rovings. This method has to date not achieved commercial success.
In order to minimize material costs, commercial pultrusion is normally carried out using polyester as the resin which is a simple thermo-set resin material so that it can be applied to the fibers from a bath and is thermo-set within the heated die. However polyester is a linear polymer which is thus not cross-linked so that it is relatively brittle so that it tends to crack when bending forces are applied to the part. This cracking is reduced by providing in the reinforcing fibers a mat material at the surface of the wall of the part so that the fibers are held in place by the transverse fibers. This avoids or reduces the tendency of the longitudinal fibers to break through the surface of the part on bending of the part. Until now, therefore, polyester resin parts have required that the mat be applied on the outside surface. Thus in a hollow cross section, a mat is applied on the surface of each wall of the part so that there is a mat on the outside and also a mat on the inside surface with the normal longitudinal fibers or rovings being placed in between the two mats. This construction significantly increases the cost of the part in that the mat is relatively expensive and two mats are required. Also the provision of two mats increases the thickness of the part and thus again increases material costs.
Non-linear resins, which may be cross-linked or amorphous such as epoxy resins, have been available for some years and are used in pultrusion; but these are significantly more expensive than polyester and thus have not achieved significant market penetration in conventional simple parts for which pultrusion is ideally suited.
Recently, improved non-linear resin materials, particularly those based on urethane, have become available which are still more expensive than polyester but are not as expensive as other cross-linked resins such as epoxy. These cross-linked urethane resins could simply be used in replacement for the conventional polyester which might lead to increased strength where required or desirable. However and in most cases the resins are of increased cost so it is necessary to consider the possibility of otherwise reducing material costs to maintain a competitive economic product while at least matching the strength of the competitive polyester product.
Mats for reinforcing pultruded parts are provided to add structural strength and in order to provide the required or expected amount of strength have a weight of fibers greater than 0.5 ounces per square foot and generally 0.75 to 1.0 ounces per square foot
Veils, which are used to provide surface characteristics and not to provide any structural strength are lighter, generally less than 0.5 ounces per square foot and typically of the order of 0.1 ounces per square foot. Conventional veils are used outside rovings or outside mats at the surface to provide an improved surface appearance or to retain the stiffer glass fibers within the resin to prevent fiber xe2x80x9cbloomxe2x80x9d or projecting fibers which can act as slivers. This latter requirement to prevent slivers is particularly important in tool handles or similar products. The retention of fibers to prevent weathering or bloom is particularly important in fenestration or similar products. Veils are well known and well used, when required for the part concerned, by persons skilled in this art and are not intended to form part of and are not considered as part of the fiber reinforcement.
It is one object of the present invention, therefore, to provide an improved pultruded part.
According to a first aspect of the invention, therefore, there is provided a pultruded part comprising:
a wall having a first surface and a second surface spaced by a thickness of the part, the wall extending longitudinally in a pultrusion direction and having a transverse width transverse to the longitudinal pultrusion direction;
fiber layers within the wall;
a non-linear resin material permeated through the fiber layers and filling the thickness between the surfaces so as to define the surfaces;
the fiber layers including at least one first layer of fibers having fibers extending only in the longitudinal pultrusion direction;
the fiber layers including one or more second layer of fibers having fibers extending both in the longitudinal pultrusion direction and transverse to the longitudinal direction;
the or each second layer of fibers having a total quantity of fibers in the layer which is less 0.5 ounces per square foot.
The longitudinal fibers referred to herein are usually glass rovings as these are inexpensive and widely available in a range of yields. However the present invention is not limited to rovings and other longitudinal bulk fibers may be used or may become available.
The reference to fibers extending both in the longitudinal pultrusion direction and transverse to the longitudinal direction is intended to include any type of mat or veil structure where the fibers are not wholly longitudinal. This includes staple fibers and continuous fibers. This includes fibers which are woven so as to extend directly longitudinal and directly transverse. This includes random non-woven mats where the fibers extend in random directions so that only portions of the fibers are transverse. This includes entangled batting. Other types of mat structure can also be included provided there is some transverse component of the fibers and provided the structure satisfies the other features as defined herein.
Where the reinforcing fibers are stated to be at or substantially at the surface, this is intended to include situations where the conventional surface veil of surface fibers is included or is not included. In some cases the surface veil is used to provide surface characteristics as is well known and the definition referred to herein assumes that this can be selected for use or not without significantly affecting the fiber reinforcement effects provided by the main body of the reinforcing fibers.
In one preferred arrangement, the wall defines a peripheral wall fully surrounding a hollow interior such that the first surface faces outwardly of the hollow interior and the second surface faces inwardly toward the hollow interior, the at least one first layer of fibers consists solely of a first layer of reinforcing fibers located substantially at the first surface and said one or more second layer of fibers are reinforcing fibers and consists solely of a second layer of reinforcing fibers located at the second surface.
In another preferred arrangement, the at least one first layer of fibers includes one first layer of reinforcing fibers located substantially at the first surface and another first layer of reinforcing fibers located substantially at the second surface and said one or more second layer of fibers comprises a layer of reinforcing fibers which is located intermediate said one first layer and said another first layer.
Preferably the resin is a urethane resin although other resins can be used provided they cross-link which allows the fibers to be located at the surface without the fibers cracking through the surface. Such resins are often known as multi-functional resins, referring to the operation of the polymers at molecular level as xe2x80x9cmulti-functionalxe2x80x9d.
Preferably the resin is a two part material set by catalytic action and is thermo-set. However other resins can also be used.
In one arrangement, the fibers of the intermediate layer form fibers of a pre-formed mat which may be of a conventional construction defined by random continuous fibers bonded or needle punched for connection. The mat may also be of the construction shown in the above published International Application assigned to Pella Corporation and on which one of the present inventors Davies is one of the named inventors.
In another arrangement, the intermediate layer of fibers comprises a plurality of cut fibers which are unsupported by mat fibers and are applied onto the second layer of fibers to be carried thereby. In this arrangement, the intermediate layer of fibers preferably consist wholly cut fibers.
Preferably the intermediate layer of fibers comprises primarily and preferably wholly straight fibers extending transverse to the longitudinal direction fully across the width of the part from one side to the other side.
Preferably the reinforcing fibers consist only of the first layer, the second layer and the intermediate layer.
Preferably the transverse layer has a weight of less than 1 oz/square foot preferably less than 0.5 oz/square foot and more preferably less than 0.25 oz/square foot and more preferably still of the order of 0.1 ounces per square foot, since it has been found that the provision of increased amounts of fiber can interfere with the cross-linking of the resin and thus provide a decreased strength rather than the increase which would normally be expected with conventional resins.
For this same reason, the transverse layer may be a scrim or mesh having openings for penetration of the resin between the fibers so as to allow effective cross-linking of the resin. It has also been found that surprisingly a veil of staple polyester fibers having a weight of as low as 0.1 oz/square foot can provide the required additional strength and/or toughness to the product.
The transverse or intermediate layer may be formed of any suitable fibers including but not limited to glass fibers, carbon fibers polymer fibers such as polyester or aramids, metal strands such as aluminum or steel or natural fibers such as cotton, jute, hemp or flax.
Natural fibers such as flax have the advantage that they are inexpensive and are to some extent porous thus allowing the resin to enter the interstices in the fibers and providing an increased bond between the fibers and the resin which can lead to reduced de-lamination and thus increased strength.
Metal strands have the advantage that they provide the required additional strength and/or toughness in the intermediate layer, but also they can provide other functions such as the required ferromagnetic effect for magnetic coupling as shown for example in U.S. Pat. No. 5,129,184 (Fish) issued Jul. 14, 1992 and/or an electrostatic charging effect for electrostatic deposition of a coating or paint material.
In view of this increased strength in the resin, the wall may include a leg portion thereof in which the reinforcing fibers consist solely of the longitudinal fibers, that is there is no transverse fibers. This is effected where the leg such as a glazing leg of a window profile has a length greater than 0.5 inches which would normally require transverse reinforcement but a length less than about 1.0 inches where there is insufficient bending moment in the leg itself to allow cracking in the leg to occur. It will be appreciated that in a non-homogeneous material such as the pultrusions defined above the bending effect at an angle is different from that within a span of the material. Thus the provision of transverse fibers within a leg or span of greater than 1.0 inches in length is required while such fibers are not necessary at an angle between two legs of shorter length.
The leg portion may have a wall that is thicker than that of the main body portion; but this is provided for balancing of forces in the pultrusion process rather than in order to provide increased strength to compensate for the absence of the mat or transverse fibers.
In one example such as for fenestration products, the main body portion defines a hollow section and the leg portion, generally a glazing leg, extends from one end at the hollow section to an opposed free end.
The urethane resin used preferably in the embodiments described hereinafter has the advantage that it is more resistant to degradation by UV and weather so that it is more suitable for fenestration products.
The construction described in the embodiments hereinafter also may have the advantage that it allows a reduced wall thickness. The use, in lower strength products such as fenestration products, conventionally of two outside perimeter mats can be reduced by one mat from two mats to one mat so that the total thickness can be reduced by at least 0.015 inch, which is the typical thickness of one mat. In addition the increased strength in the resin itself may allow a further reduction so that typically a conventional range in inches of polyester resin construction of 0.070 to 0.180 for different end uses can be reduced to a range of 0.030 to 0.120. A thickness even as low as 0.025 may also be possible for products such as fenestration products which require lower structural strength and a thickness of the order of 0.080 may be possible for products such as ladder rails or tool handles which require higher structural strength. In particular the higher strength structural products often include a third mat along the center and thus the three mats of the conventional product can be reduced to one mat or veil in the arrangement described above thus yet further reducing the thickness. This reduction in mat content also increases the proportion of longitudinal fibers or rovings and this also has the advantage that the longitudinal stiffness of the part as provided by the longitudinal fibers is also increased. Thus a ladder rail may be reduced typically in thickness from 0.125 to 0.105 inch with an increase in strength.
In one advantageous arrangement, the transverse fibers are formed of metal strands which provide both transverse strength and the characteristic of electrical conductivity and/or ferromagnetism for the part.